To look at a box of Kellogg’s Corn Flakes is to look at the triumph of several defining elements of American life: the conflation of food and salvation, the establishment of modern business systems and mass production, the growth and acceptance of prepackaged food and self-service markets, the gospel of convenience and the powerful eruption of mass advertisement directed at women and children. It is also a relic of the mutually resentful, rancorous relationship between two men: Dr. John Kellogg and his younger brother, Will.

The brothers, two of their father’s 16 children, grew up as Seventh-day Adventists. The family moved to Battle Creek, Michigan, where two of the sect’s founders, Ellen G. White and James White, had set up a press whose publications fused moral integrity, spiritual salvation and dietary reform. The couple took young John under their wing, putting him to work on their magazine, The Health Reformer. Seeing a future role for him in their struggling Western Health Reform Institute, they steered him toward medicine and supported his studies. He emerged a doctor, strong in the belief that a vegetarian diet, exercise, and frequent bowel movements were the key to good health.

John was installed as the institute’s medical director and transformed it from a rinky-dink operation, run out of a converted home, into the Battle Creek Sanitarium, a huge medical complex centered on diet and exercise. It comprised a laboratory, experimental kitchen, vegetable gardens, exercise and water-therapy rooms, surgical theater, auditorium and a well-appointed resort for wealthy neurasthenics.

Meanwhile, a disgruntled Will, who had been roped into the family broom business, threw over the despised trade and attended business college, mastering accounting and business contract writing. John hired him to manage the institute’s publishing and food business — and to serve as his lackey.

Markel gives dismaying examples of John’s cruelty to Will when they were boys, treatment that seems to have groomed the younger Kellogg for more than 20 years of oppression. John, though an excellent doctor and charismatic leader, was a tyrant, making his brother his “personal valet, shining his white shoes, trimming and shaping his beard each morning with a straight razor, and following John into the bathroom to take . . . dictation while the doctor unloaded one of his four to five daily bowel movements.”

Despite these and other humiliating duties, Will emerged as a genius of business management, eventually overseeing every aspect of the sanitarium, though both the Adventists and his brother threw countless obstacles in his way — both parties seeing, in their different ways, the institute’s work as a mission and not as a business. John’s differences with the Adventists finally ended with his seizing control of the institute in tricky, well-described legal maneuvers.

For years, the Kelloggs had tried to create a ready-to-eat, nutritious, grain-based breakfast food — one whose tough kernels would not break one’s teeth. Markel gives a detailed, fascinating account of how — and who — achieved their goal: a (reasonably) palatable flaked-grain cereal. He also describes the nefarious role played by C.W. Post, a charity patient who worked in the Sanitarium’s experimental kitchen and walked off with the Kelloggs’ recipes and processes — from which he made a fortune.

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The theft was less troubling to John, who was interested chiefly in furthering dietary reform; Will, the businessman, was outraged. It was he who finally developed the crisp, delicious cornflakes that became America’s favorite breakfast. In a series of fairly unpleasant negotiations with John, he managed to set up his own company to manufacture and sell his version of cornflakes — a deal that was followed by one acrimonious, litigious chapter after another in the brothers’ relationship.

In addition to capturing the personalities of the two brothers, Markel does an extraordinary job covering the many complex dimensions of this story, including John’s later, unfortunate embrace of his own idiosyncratic version of the pseudoscience of eugenics, “a mishmash theory combining elements of Lamarckism, Darwinism, biologic living, and Christian faith.” Among the broader developments “The Kelloggs” goes into are the advent of self-service grocery stores, improved packaging and mass advertising. Will’s ceaseless and ingenious promotional campaigns included one which prompted women to wink at their grocers and another which put Kellogg’s Corn Flakes up in neon lights in Times Square.

Markel, the author of three previous, well-received histories has, by reaching into a simple box of cornflakes, come up with a rich and satisfying account of the lives, work and enmity of two warring brothers and of a pivotal epoch in American history.